Audio Systems: feedback, heavy duty battery, amp output

Question
im trying to install a stereo and amp in my truck (both are kenwwod)the amp is 800 watt max and im running 2 12" speakers in a box.when i bridge the amp i get a rapid thumping sound from the speakers. what am i doing wrong?  

Answer
Dean,
With an 800 watt amp you must have very large 12 volt supply wires and a heavy duty battery, plus an alternator of at least 120 amp output. The thumping sound from the speakers when the amp is bridged, may be due to the amp shutting down because of not having enough operating current. you may also need a ground loop isolator installed in the RCA lines to the amp.

TOM,
T&D ELECTRONICS
tdeser@zoominternet.net